Fluid pressure boosting type brake system

ABSTRACT

A fluid pressure boosting type brake system includes a fluid pressure source including a fluid pump and a pressure tank connected to the pump, and a control valve capable of controlling the output pressure from the fluid pressure source to a fluid pressure corresponding to the degree of brake operation to output it. In this brake system, the fluid pump can be driven in accordance with the consumption of fluid pressure in a brake device, thereby insuring a reliable sufficient fluid pressure in the fluid pressure source.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid pressure boosting type brakesystem comprising a fluid pressure source including a fluid pump and apressure tank connected to the pump, and a control valve capable ofcontrolling an output pressure from the fluid pressure source to a fluidpressure corresponding to a degree brake of operation to output thesame.

2. Description of the Related Art

Such brake systems are already known, for example, from Japanese PatentApplication Laid-open Nos. 274958/92 and 345568/92.

In the brake system disclosed in Japanese Patent Application Laid-openNo. 274958/92, the operation of the fluid pump is controlled by apressure switch which is turned ON, when the fluid pressure in thepressure tank becomes equal to or less than a predetermined value.Therefore, when the pressure switch malfunctions, the fluid pump may notbe operated, resulting in a reduction in brake assisting force. In thebrake system disclosed in Japanese Patent Application Laid-open No.345568/92, the fluid pressure in the pressure tank is detected by apressure sensor in addition to the pressure switch, thereby judgingwhether or not the pressure switch is normal. However, if a circuit forcontrolling the operation of the fluid pump, under reception of thedetection values detected by the pressure switch and the pressuresensor, malfunctions, then the fluid pump may fail to be operated,resulting in a reduction in brake assisting force.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a fluidpressure boosting type brake system, in which the fluid pump can bedriven in accordance with the consumption of a fluid pressure in a brakedevice to reliably insure a sufficient fluid pressure in the fluidpressure source.

To achieve the above object, the brake system according to the presentinvention comprises a fluid pressure source including a fluid pump and apressure tank connected to the pump, and a control valve capable ofcontrolling an output pressure from the fluid pressure source to a fluidpressure corresponding to the degree of brake operation to output thesame, wherein the system further includes a brake operation detectingmeans for detecting a brake operation, and a consumed-pressurecorrespondence driving means for outputting a driving signal indicativeof a command to drive the fluid pump for each preset time for apredetermined period, while the brake operation is detected by the brakeoperation detecting means.

With the above arrangement, the fluid pump is driven in anON/OFF-repeated manner in accordance with the consumption of fluidpressure corresponding to the brake operation. Thus, even if thepressure detector is not provided, or even if a pressure detector getsout of order, the fluid pressure pump can be driven to reliably insure asufficient fluid pressure in the fluid pressure source.

The brake system according to the present invention, further including apressure detector for detecting a fluid pressure in the pressure tank, adetected-pressure correspondence driving means provided in parallel tothe consumed-pressure correspondence driving means and capable ofoutputting a driving signal indicative of a command to drive the fluidpump in accordance with a detection value detected by the pressuredetector, and a prohibiting-signal outputting means for outputting aprohibiting signal indicative of a command to prohibit the output of thedriving signal from the consumed-pressure correspondence driving meansin a state in which the detected-pressure correspondence driving meanscan output the driving signal.

With the above arrangement, if the control based on the detection valuedetected by the pressure detector is made impossible, then the fluidpump can be driven, while being suppressed in frequency of operation inaccordance with the consumption of fluid pressure, thereby enhancing thereliability for supply of the fluid pressure.

The brake system, in addition, includes power circuits individuallyconnected to the consumed-pressure correspondence driving means and thedegree-of detected pressure correspondence driving means, respectively.

With the above arrangement, a completely double redundant circuit can beconfigured to further enhance the reliability.

In the brake system, there is provided a fluid pressure boosting brakesystem, comprising a fluid pressure source, including a fluid pump andan accumulator connected to the pump, and a control valve capable ofcontrolling an output pressure from the fluid pressure source to a fluidpressure, corresponding to a brake operation quantity, to output thesame, wherein the brake system further includes brake operationdetecting means for detecting a brake operation, a motion parameterdetecting means for detecting a longitudinal motion parameter of avehicle, and a driving means capable of outputting a driving signalindicative of a command to drive the fluid pump for a time determined onthe basis of the motion parameter during braking.

With the above arrangement, the fluid pump is driven in accordance withthe consumption of fluid pressure corresponding to the brake operation.Thus, even if a pressure detector is not provided, or even if a pressuredetector is provided and gets out of order, the fluid pressure can bedriven to reliably insure a sufficient fluid pressure in the fluidpressure source.

The brake system further includes a pressure detector for detecting afluid pressure in the pressure tank, and a normal-state detecting meansfor detecting the pressure detector being in a normal state, the drivingmeans being arranged such that the following two states 1) and 2) can beswitched over: a state 1) in which the driving means outputs the drivingsignal indicative of a command to drive the fluid pump for a timedetermined on the basis of the motion parameter during braking, when thepressure detector is in an abnormal state, and a state 2) in which thedriving means outputs the driving signal indicative of a command todrive the fluid pump on the basis of a detection value detected by thepressure detector, when the pressure detector is in a normal state.

With the above arrangement, if the control based on the detection valuedetected by the pressure detector becomes impossible, due to a troubleof the pressure detector, the fluid pump can be driven in accordancewith the consumption of fluid pressure to provide an enhancedreliability for supply of the fluid pressure.

The above and other objects, features and advantages of the inventionwill become apparent from the following description of preferredembodiments, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a liquid pressure boosting type brakesystem according to a first embodiment of the present invention;

FIG. 2 is a diagram of an arrangement of a pump-operation control unit;

FIG. 3 is a flow chart illustrating a main routine for judgement of atrouble of a pressure detector;

FIG. 4 is a flow chart illustrating a sub-routine for detection of avariation in liquid pressure;

FIG. 5 is a flow chart illustrating a sub-routine for forcedly driving apump;

FIG. 6 is a diagram illustrating an output characteristic of thepressure detector;

FIG. 7 is a timing chart for judgement of a trouble of the pressuredetector;

FIG. 8 is a timing chart for judgement of a trouble of the pressuredetector at the restart after the judgement of the trouble;

FIG. 9 is a timing chart for driving the pump;

FIG. 10 is a diagram of an arrangement of a pump-operation control unitin a second embodiment;

FIG. 11 is a map in which the pump driving time is determined inaccordance with the deceleration;

FIG. 12 is a timing chart for driving the pump;

FIG. 13 is a map in which the pump driving time is determined inaccordance with the vehicle speed in a modification to the secondembodiment; and

FIG. 14 is a timing chart for driving the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention applied to a liquid pressureboosting type brake system in a vehicle will now be described inconnection with FIGS. 1 to 9.

Referring first to FIG. 1, a reaction force generating means 2, forexhibiting a spring force opposing a depression force on a brake pedal1, is connected to the brake pedal 1 through a depression force sensor 3for detecting the brake-operation oparation. During normal braking, theoutput pressure from a liquid pressure source 5, as a fluid pressuresource, is controlled by a control valve 4 in accordance with the degreeof brake-operation detected by the depression force sensor 3, and anoutput liquid pressure, from the control valve 4, is applied to a wheelbrake B. A braking liquid pressure of the wheel brake B can be alsomaintained, or controlled, by a normally-opened type solenoid inletvalve 6 and a normally-closed type solenoid outlet valve 7 which areprovided, in correspondence to the wheel brake B, to effect an anti-lockcontrol.

The liquid pressure source 5 includes a liquid pump 9, as a fluidpressure pump driven by a motor 8, to pump a working liquid from areservoir R, a pressure tank 10 (an accumulator in this embodiment)connected to the liquid pump 9, and a pressure detector 11 for detectinga liquid pressure accumulated in the accumulator 10.

The control valve 4 includes a housing 13, having a cylinder bore 12closed at its axially one end, a spool 14, slidably received in thecylinder bore 12, a reaction piston 15, slidably received in thecylinder bore 12, while abutting against the spool 14, and a linearsolenoid 16 mounted to a side surface of the axially other end of thehousing 13 to exhibit a driving force for urging the reaction piston 15in one axial direction thereof.

An output chamber 17 is defined between one end of the spool 14 and oneend wall of the cylinder bore 12, and a spring 18 is accommodated in theoutput chamber 17 for biasing the spool 14 in the other axial direction.

An annular output pressure working chamber 19 is defined by an innersurface of the cylinder bore 12, the spool 14 and the reaction piston15. The chamber 19 faces a front surface of the reaction piston 15. Acommunication passage 20 is provided in the spool 14, over the axiallyentire length thereof, to lead to the output chamber 17, and acommunication hole 21 is provided in the reaction piston 15 forpermitting communication of the communication passage 20 with the outputpressure working chamber 19. A liquid pressure force is applied to thereaction piston 15 in the other axial direction (i.e., rightwardly asviewed in FIG. 1) by a liquid pressure in the output pressure workingchamber 19 leading to the output chamber 17, so that the spool 14 ismoved to follow the reaction piston 15 by a spring force of the spring18.

The linear solenoid 16 moves a driving rod 22 axially by a thrustcorresponding to an applied quantity of electricity, so that the drivingrod 22 coaxially abuts against a piston rod 15a integrally provided onthe reaction piston 15. Thus, a thrust of the linear solenoid 16 isapplied to the spool 14 in the one axial direction, while a liquidpressure force from the output pressure working chamber 19 is applied tothe spool 14 in the other axial direction, so that the spool 14 is movedaxially by a balance between the thrust and the liquid pressure force.

The housing 13 has an output port 23, a release port 24 and an inputport 25 which are provided therein at distances from one another insequence from one of the axial ends. The output port 23 normallycommunicates with the output chamber 17, the release port 24 leads tothe reservoir R, and the input port 25 leads to the liquid pressuresource 5.

The spool 14 is provided with a first valve bore 26 capable ofpermitting the communication between the input port 25 and thecommunication passage 20, and with a second valve bore 27 capable ofpermitting the communication between the release port 24 and thecommunication passage 20. The arrangement of the valve bores 26 and 27is determined such that when the spool 14 has been moved in one of itsaxial directions, the first valve bore 26 is in a state in which itpermits communication between the input port 25 and the communicationpassage 20, whereas when the spool 14 has been moved in the other axialdirection, the second valve bore 27 is in a state in which it permitscommunication between the release port 24 and the communication passage20.

The wheel brake B includes a cylinder 30 and a braking piston 31slidably received in the cylinder 30, so that a braking force, exhibitedby the movement of the braking force 31, corresponds to a liquidpressure applied to braking liquid pressure chamber 32 between cylinder30 and braking piston 31.

The normally-opened type solenoid inlet valve 6 is interposed betweenthe braking liquid pressure chamber 32 in the wheel brake B and theoutput port 23 in the control valve 4. The normally-closed type solenoidoutlet valve 7 is interposed between the reservoir R and the brakingliquid pressure chamber 32 in the wheel brake B.

The operation of the control valve 4, i.e., the quantity of electricityapplied to the linear solenoid 16 is controlled by liquid pressurecontrol unit 28 in accordance with the degree of brake operationdetected by the depression force sensor 3. The switch-over of theenergization and deenergization of the normally-opened type solenoidinlet valve 6 and the normally-closed type solenoid outlet valve 7 isalso controlled by liquid pressure control unit 28.

The operation of the liquid pump 9, in liquid pressure source 5, i.e.,the operation of the motor 8, is controlled by a pump operation controlunit 29₁. A brake switch 33 serving as a brake-operation detecting meansfor detecting the braking operation, i.e., the operation of the brakepedal 1 and the pressure detector 11, in the liquid pressure source 5,are connected to the pump operation control unit 29₁.

Referring to FIG. 2, the motor 8, for driving the liquid pump 9, isconnected to a power source 50 through a relay switch 35s and a fuse 34.A relay coil 35c, constituting a relay together with the relay switch35s, is also connected to the power source 50 through the fuse 34. Whenthe relay coil 35c is energized, the motor 8 is operated. When the relaycoil 35c is deenergized, the operation of the motor 8 is stopped.

The energization and deenergization of the relay coil 35c are controlledby the pump-operation control unit 29₁. The pump-operation control unit29₁ includes a transistor 37 connected to the relay coil 35c, through aconnector 36, a central processing unit CPU, for controlling the ON-OFFof the transistor 37, a transistor 39 connected to the relay coil 35c,through a connector 38, a consumed-pressure correspondence drive means40 for controlling the ON-OFF of the transistor 39, and power circuits41 and 42, individually connected to the central processing unit CPU andthe consumed-pressure correspondence drive means 40.

The central processing unit CPU has a processing function, as adetected-pressure correspondence drive means 43, for controlling theON-OFF of the transistor 37 to output a driving signal indicative of acommand to drive the liquid pump 9 in accordance with a detection valuedetected by the pressure detector 11, and a processing function, as aprohibiting signal generating means 44, for generating a prohibitinglow-level signal, indicative of a command to prohibit the output of thedriving signal from the consumed-pressure correspondence drive means 40,when the detected-pressure correspondence drive means 43 is in a statecapable of outputting the driving signal. A detection signal, from thepressure detector 11, is supplied through the connector 36 and via afilter/buffer 45 to the central processing unit CPU, and the brakeswitch 33, connected to the power source 50 through the fuse 49, isconnected to the central processing unit CPU through the connector 38.The power source 50 is connected to the power circuit 41 through thefuse 46, an ignition switch 47 and the connector 36, and the powersource 50 is also connected to the power circuit 41 through the fuse 48and the connector 36.

The prohibiting signal generating means 44 outputs the prohibitinglow-level signal to the consumed-pressure correspondence drive means 40,when the detected-pressure correspondence drive means 43 is in the statecapable of outputting the driving signal, i.e., in a state in whichthere are no trouble of the power circuit 41 and no trouble of thepressure detector 11. In the prohibiting signal generating means 44, thetrouble of the pressure detector 11 is detected by a procedure whichwill be described below.

As shown in FIG. 3, at a first step S1, it is judged whether or not aflag F_(D) is equal to "1". The flag F_(D) is intended to demand thedriving of the liquid pump 9 irrespective of the detection valuedetected by the pressure detector 11 in detecting the trouble of thepressure detector 11. The flag F_(D) equal to "1" indicates a state inwhich the driving of the liquid pump 9 is demanded. If F_(D) =0, theprocessing is advanced to a second step S2. On the other hand, if F_(D)=1, the processing is advanced to a third step S3.

At the second step S2, a variation in liquid pressure is detectedaccording to a sub-routine shown in FIG. 4. At a first sept M1 in thissub-routine, it is judged, on the basis of the driving signal from thedetected-pressure correspondence drive means 43, whether or not theliquid pump 9 is in operation. If it is decide(that the liquid pump 9 isin operation, the count value N_(C) of a counter is set at "0" at aneighth step M8. This counter counts the number of braking operations.

If it is decided at the first step M1 that the liquid pump 9 is out ofoperation, the processing is advanced to a second step M2, where it isjudged whether or not the braking operation has been started, i.e.,whether or not a detection signal from the brake switch 33 has beengiven. At the start of the braking operation, "1" is added to the countvalue N_(C) at a third step M3. If it is decided at a next fourth stepM4 that the count value N_(C) is equal to "1", i.e, that the number ofbraking operations is one, then the currently detected liquid pressurevalue is latched as a first reference liquid pressure P_(BF),progressing to a sixth step M6. Even when it is decided at the secondstep M2 that the braking operation is not started, as well as when it isdecided at the fourth step M4 that N_(C) ≠1, then the processing isadvanced to the sixth step M6.

At the sixth step M6, it is judged whether or not the braking operationhas been ended, i.e., whether or not the detection signal from the brakeswitch 33 is fallen. At the end of the braking operation, the processingis advanced to a seventh step M7. It is judged at this seventh step M7whether or not a decrement of the detected liquid pressure is equal toor more than a predetermined value ΔP₁, e.g., 4 kg/cm². That is, thedetected liquid-pressure P, at the end of the braking operation., iscompared with the first reference liquid pressure P_(BF) latched at thefifth step M5. If (P_(BF) 31 P)≧ΔP₁, then the processing is advanced tothe eighth step M8, and if (P_(BF) -P)≧ΔP₁, then the processing isadvanced to the ninth step M9.

In the ninth step M9, it is judged whether or not the count value N_(C)is equal to "5". In N_(C) =5, the count value N_(C) is fixed at "5" at atenth step M10, and then, the flag F_(D) is set at "1" at a 11th stepM11.

With such sub-routine shown in FIG. 4, the detected liquid pressurevalue at the start of the braking operation is stored as the referenceliquid pressure PBF during non-operation of the liquid pump 9, and whena state in which the decrement: of the detected liquid pressure value,during continuation of the braking-operation, is lower than thepredetermined value ΔP₁, as a result of comparison of the detectedliquid pressure P, at the end of the braking operation with the firstreference liquid pressure P_(BF), has been continued five times or more,the flag F_(D), for forcedly driving the liquid pump 9, is set at "1".In other words, when a state in which the variation in output from thepressure detector 11 is lower than the predetermined value ΔP₁,irrespective of the consumption of liquid pressure with the brakingoperation, has been continued five times or more, the liquid pump 9 isforcedly driven.

At the third step S3, in the main routine shown in FIG. 3, a sub-routineshown in FIG. 5 is carried out. At a first step N1 in FIG. 5, the liquidpump 9 is driven irrespective of the detection value detected by thepressure detector 11. At a second step N2, it is judged whether or notthe driving of the liquid pump 9 is a first driving. If it is the firstdriving, the currently detected liquid pressure value is latched as asecond reference liquid pressure P_(BF) at a third step N3. At a fourthstep N4, a timer for counting the time of driving of the liquid pump 9,when the flag F_(D) is equal to "1", is reset, progressing to a sixthstep N6. If it is decided at the second step N2 that the driving of theliquid pump 9 is a second or more driving, the time T counted by thetimer is counted up at a fifth step N5, progressing to the sixth stepN6.

At the sixth step N6, it is judged whether or not the detected liquidpressure value has been increased by a second predetermined value ΔP₂,e.g., 4 kg/cm² or more from the second reference liquid pressure P_(EP),before the time counted by the timer reaches a preset time T₀, e.g., 3seconds. If it is decided that the detected liquid pressure value hasbeen increased by the second predetermined value ΔP₂, or more, withinthe preset time T₀, a counter and the timer are reset, while at the sametime, the flag F_(D) is set at "0", at the seventh step N7.

If it is decided at the sixth step N6 that the variation in detectedliquid pressure value P from the second reference liquid pressureP_(BP), within the preset time T₀, is less than the second predeterminedvalue ΔP₂, then a flag F_(F) is set at "1" at an eighth step N8, and theflag F_(D) is set "0" at a ninth step N9.

With such sub-routine shown in FIG. 5, when the variation in detectedliquid pressure value is less than the second predetermined value ΔP₂within the preset time T_(O) from the start of the driving of the liquidpump 9, when the liquid pump 9 is being forcedly driven as a result ofthe flag F_(D) becoming equal to "1", the flag F_(F) is set at "1" onthe basis of the decision that the pressure detector 11 is out of order,i.e., has a trouble.

Again, in the main routine shown in FIG. 3, it is judged at a fourthstep S4 whether or not the flag F_(F) is equal to "1", after thesub-routine of the second step S2 has been carried out. If F_(F) =1, itis judged at a fifth step S5 whether or not it is immediately after thestart, i.e., whether or not it is immediately after the turn-ON of theignition switch 47. If it is immediately after the start, the processingis advanced to a sixth step S6. If it is decided at the fourth step S4that F_(F) ≠1, as well as if it is decided at the fifth step S5 that itis not immediately after the start, the processing is advanced to aninth step S9.

At the sixth step S6, the detected liquid pressure value, at that time,is latched as a third referenced liquid pressure P_(BC), and at a nextseventh step S7, it is judged whether or not the detected liquidpressure value is varied from the third reference liquid pressure P_(BC). If there is a variation in liquid pressure, the flag F_(F) is set at"0"; the counter and timer are reset and further, an alarm lamp (notshown) turned ON at the start, i.e., at the turn-ON of the ignitionswitch 47 is turned OFF, all at an eighth step S8. If it is decided atthe seventh step S7 that there is no variation in liquid pressure, theprocessing is advanced to the ninth step S9.

At the ninth step S9, it is diagnosed according to a sub-routine (notshown) whether or not the pressure detector 11 is out of order, i.e.,has a trouble, while remaining at a high or low level. The outputvoltage from the pressure detector 11 is determined so as to read 0.5 V,for example, when the liquid pressure is 0 kg/cm², and to read 4.5 V,for example, when the liquid pressure is 200 kg/cm². In thissub-routine, if the output voltage from the pressure detector 11 is lessthan 0.5 V or exceeds 4.5 V, then it is diagnosed that the pressuredetector 11 is out of order. If it is decided at a tenth step S10 thatthe trouble has been detected, then the alarm lamp is turned ON and atthe same time, an error code indicating that the pressure detection 11is out of order in a high or low level sticking state is set at an 11thstep S11. This error code is not eliminated even by the turn-OFF of theignition switch 47.

After the sub-routine of the third step S3 has been carried out, it isjudged at a 12th step S12 whether or not the flag F_(F) is equal to "1".If F_(F) ≠1, the processing is advanced to the ninth step S9. On theother hand, if F_(F) =1, the alarm lamp is turned ON and at the sametime, an error code indicating that the pressure detector 11 is out oforder, including the fact that the flag F_(F) is equal to "1", is set ata 13th step S13. This error code is not eliminated even by the turn-OFFof the ignition switch 47.

A timing chart according to such a procedure of detecting the trouble ofthe pressure detector 11 is as shown in FIG. 7. Before the pressuredetector 11 gets out of order, the currently detected liquid pressurevalue is latched as a first reference liquid pressure P_(BF1) at a timepoint of the start of the braking operation, i.e., at a time point t₁when an output signal from the brake switch 33 is risen. The detectedliquid pressure value P, at a time point of the end of the brakingoperation, i.e., at a time point t₂ when the output signal from thebrake switch 33 is fallen, is compared with the first reference liquidpressure P_(BF1). From the fact that P_(BF1) -P>ΔP₁, it is decided thatthere is a variation in liquid pressure.

Then, if the pressure detector 11 gets out of order at a time point t₃,the currently detected liquid pressure value is latched as a firstreference liquid pressure P_(BF2) at a time point t₄ of the brakingoperation after the time point t₃. Then, the detected liquid pressurevalue P is compared with the first reference liquid pressure P_(BF2) ata time point t₅ of the end of the braking operation. If P_(BF2) -P<ΔP₁,the count number Nc in the counter is equal to "1". Five brakingoperations all told are carried out between the time points t₄ and t₁₃.If it is decided that all the results of comparison of the liquidpressures at time points t₅, t₇, t₉, t₁₁ and t₁₃ of the ends of thebraking operations are (PBF₂ -P<ΔP₁) and that there is no variation inliquid pressure, i.e., if the count number Nc in the counter reaches "5"the flag F_(D) is equal to "1", and the forced driving of the liquidpump 9 is started, while at the same time, the currently detected liquidpressure value is latched as a second reference liquid pressure P_(BP),and the counting in the timer is started.

Thereafter, if the variation in detected liquid pressure value P is lessthan a second predetermined value ΔP₂, even at a time point t₁₄ after alapse of the preset time T₀ from the start of the forced driving of theliquid pump 9, the flag F_(d) is set at "0", and the forced driving ofthe liquid pump 9 is stopped, while at the same time, the flag F_(F) isset at "1", and the alarm lamp is turned ON. When the detected liquidpressure value P is increased to a level equal to or more than thesecond predetermined value ΔP₂, as shown by a dashed line in FIG. 7,before a lapse of the preset time T₀, the driving of the liquid pump 9is stopped at that time point, while at the same time, the counting inthe timer is stopped, and the flag F_(F) remains equal to "0", i.e., thealarm lamp is not turned ON.

At the restart, after the judgment of the trouble, the flag F_(F)remains equal to "1", if the detected liquid pressure value P is notvaried relative to a third reference liquid pressure PB_(C), as shown inFIG. 8, immediately after such restart, i.e., immediately after theturn-ON of the ignition switch 47. On the other hand, when the detectedliquid pressure value P is varied, as shown by a dashed line in FIG. 8,the flag F_(F) is set at "0" at that time point, and correspondingly,the alarm lamp is turned OFF.

Referring again to FIG. 2, the consumed-pressure correspondence drivingmeans 40 includes a first timer circuit 51 to which a signal from thebrake switch 33 is applied through the connector 38 and which isconnected to the power circuit 42, and a second timer circuit 52 towhich a signal from the first timer circuit 51 is applied and which isconnected to the power circuit 42. The transistor 39 is turned ON inresponse to an output signal from the second timer circuit 52 broughtinto a high level, and a prohibiting signal outputted from theprohibiting signal generating means 44 is applied to the second timercircuit 52.

The power source 50 is connected to the power circuit 42 through thefuse 46, the ignition switch 47 and the connector 38 and also throughthe fuse 48 and the connector 38.

The first timer circuit 51 repeatedly outputs a high level signal at apredetermined period T₁ during the braking operation, i.e., during theturn-ON of the brake switch 33. The second timer circuit 52 outputs asignal which is sustained at a high level for a preset time T₂, inresponse to the reception of the high level signal from the first timercircuit 51 in a state in which no low level prohibiting signal isreceived thereinto from the prohibiting signal generating means 44,i.e., in a state in which a signal received thereinto from theprohibiting signal generating means 44 is of a high level. The presettime T₂ is set shorter than the period T₁ (T₂ <T₁).

Therefore, in a state in which no low level prohibiting signal isoutputted from the prohibiting signal generating means 44, a high leveldriving signal, sustained for the preset time T₂, is outputted at thepredetermined period T₁ during the braking operation, thereby allowingthe transistor 39 to be repeatedly turned ON and OFF, so that the motor8 and, thus, the liquid pump 9 may be operated in an ON/OFF-repeatedmanner.

The operation of the first embodiment will be described below withreference to FIG. 9. For a period T_(A) in which a low level prohibitingsignal is outputted from the prohibiting signal generating means 44 in astate in which the detected-pressure correspondence driving means 43 canoutput a driving signal, the output of the driving signal from thesecond timer circuit 52 in the consumed-pressure correspondence drivingmeans 40 is prohibited, and the motor 8 and, thus, the liquid pump 9 aredriven in response to the output of the driving signal from thedetected-pressure correspondence driving means 43 in correspondence tothe detection value detected by the pressure detector 11, therebyallowing the liquid pressure to be varied.

For a period T_(B), in which the high level signal, from the prohibitingsignal generating means 44, is received into the second timer circuit 52in the consumed-pressure correspondence driving means 40 in a state inwhich there are no troubles in the central processing unit CPU itself,the power circuit 41 and the pressure detector 11 and in which thedetected-pressure correspondence driving means 43 can output the drivingsignal, a high level signal, sustained for the preset time T₂, isoutputted from the second timer circuit 52 in response to the output ofa high level signal at every given period T₁ from the first timercircuit 51, during the braking operation, i.e., while the brake switch33 is conducting. In response to this, the motor 8 and, thus, the liquidpump 9 are operated in an ON/OFF-repeated manner, so that the liquidpressure can be accumulated in the pressure tank 10 in accordance withthe consumption of the liquid pressure.

Thus, if the operation of the liquid pump 9, based on the detectionvalue detected by the pressure detector 11, is made impossible, due totroubles of the central processing unit CPU itself, the power circuit 41and the pressure detector 11, then the liquid pump 9 can be driven bythe consumed-pressure correspondence driving means 40 in accordance withthe consumption of the liquid pressure corresponding to the brakingoperation, irrespective of the detection value detected by the pressuredetector 11. Therefore, even if the operation of the liquid pump 9,based on the detection value detected by the pressure detector 11, isdifficult, a sufficient liquid pressure can be insured by the pressuretank 10, and a reduction in brake assisting force can be prevented.Moreover, because the driving of the liquid pump 9 by theconsumed-pressure correspondence driving means 40 is performed in theON/OFF-repeated manner, the frequency of operation of the liquid pump 9can be suppressed to the minimum even during a pumping braking with adriver's foot remaining on the brake pedal 1, thereby providing anenhanced reliability for supply of the liquid pressure to the controlvalve 4.

Further, a circuit including the detected-pressure correspondencedriving means 43 and a circuit including the consumed-pressurecorrespondence driving means 40, excluding the connectors 36 and 38, areprovided in parallel to each other, and the power circuits 41 and 42 areconnected to the detected-pressure correspondence driving means 43 andthe consumed-pressure correspondence driving means 40, respectively.Therefore, the reliability can be further enhanced by construction ofthese circuits into a completely double redundant circuit.

FIG. 10 illustrates a pump-operation control unit according to a secondembodiment of the present invention. The pump-operation control unit292, for controlling the energization and deenergization of the relaycoil 35c, includes a transistor 37 connected to the relay coil 35c,through a connector 36', a central processing unit CPU' for controllingthe turn ON and OFF of the transistor 37, a transistor 39 connected tothe relay coil 35c through a connector 38, a consumed-pressurecorrespondence driving means 40 for controlling the turn ON and OFF ofthe transistor 39, and power circuits 41 and 42 individually connectedto the central processing unit CPU' and the consumed-pressurecorrespondence driving means 40.

The central processing unit CPU' has processing functions as a drivingmeans 54 for controlling the turn ON and OFF of the transistor 37 tooutput a driving signal for driving the liquid pump 9, a prohibitingsignal generating means 44₁, for outputting a low level prohibitingsignal for prohibiting the output of the driving signal from the secondtimer circuit 52 in the consumed-pressure correspondence driving means40 in a state in which there are no troubles of the central processingunit CPU' itself and the power circuit 41 and in which the drivingsignal can be outputted from the driving means 54, and a normal-statedetector 44₂ for detecting whether or not the pressure detector 11 is ina normal operation. A detection signal, detected by the pressuredetector 11, is applied from the connector 36' through a filter/buffer45 into the central processing unit CPU', and the brake switch 33 isconnected to the central processing unit CPU' through a connector 38.Further, a vehicle speed detector 53, as a motion parameter detectingmeans for detecting a vehicle speed V as a longitudinal vehicle motionparameter, is connected to the central processing unit CPU' through theconnector 36'.

The prohibiting signal generating means 44₁ has the same functions asthe processing functions of the prohibiting signal generating means 44in the first embodiment, but excluding the trouble judging function ofthe pressure detector 11. In a state in which there are no troubles ofthe central processing unit CPU' itself and the power circuit 41 and thelike, a low level prohibiting signal is applied to the second timercircuit 52 in the consumed-pressure correspondence driving means 40 onthe basis of the fact that the output of the driving signal from thedriving means 54 is possible. The normal-state detector 44₂ detects anormal state of the pressure detector 11 according to the procedureshown in FIGS. 3 to 9 in the previously-described first embodiment, andapplies a high level signal to the driving means 54, when it is decidedthat the pressure detector is in the normal state.

The driving means 54 outputs a different driving signal, in response tothe reception of the signal from the normal-state detector 44₂, tocontrol the turn ON and OFF of the transistor 37. When a low levelsignal is received into the driving means 54 from the normal-statedetector 44₂, because it is judged that the pressure detector 11 is inan abnormal state, a driving signal is outputted for driving the liquidpump 9 for a time T₃ determined on the basis of the vehicle speed Vduring braking. When a high level signal is received into the drivingmeans 54 from the normal-state detector 44₂, because it is judged thatthe pressure detector 11 is in the normal state, a driving signal isoutputted for driving the liquid pump 9 on the basis of a detectionvalue detected by the pressure detector 11.

The driving means 54 has a reap previously established therein, as shownin FIG. 11. This map is such that the driving time T₃ for the liquidpump 9 is determined in accordance with the deceleration α of thevehicle, wherein the driving time T₃ becomes gradually larger, as thedeceleration α is larger, i.e., as the amount of liquid pressureconsumed is larger due to application of a larger braking force. Thedeceleration α is determined according to the following equation:α=(V_(ON).sup.˜ V_(OFF))/(t_(ON) -t_(OFF)), wherein V_(ON) and t_(ON)represent a vehicle speed and a time point at the start of a brakingoperation, respectively, and V_(OFF) and t_(OFF) represent a vehiclespeed and a time point at the end of the braking operation,respectively.

With the second embodiment, in a state in which it is decided by thenormal-state detecting means 44₂ that the pressure detector 11 isnormal, the driving signal is outputted from the driving means 54 inaccordance with the detection value detected by the pressure detector11, thereby driving the liquid pump 9. On the other hand, if it isdecided by the normal-state detecting means 44₂ that the pressuredetector 11 is abnormal, then the driving signal sustained for thedriving time T₃, determined by the deceleration α is outputted from thedriving means 54 at a time point when the braking operation is ended.Therefore, even if the pressure detector gets out of order, the pressurepump 9 can be operated in correspondence to the amount of liquidpressure consumed, thereby insuring a sufficient liquid pressure in thepressure tank 10 to prevent a reduction in brake assisting force.

Even if the driving of the liquid pump 9 by the driving means 54 isdifficult, due to a trouble of the central processing unit CPU' itself,or due to a trouble of the power circuit 41 and the like, the liquidpump 9 can be driven by the consumed-pressure correspondence drivingmeans 40 in accordance with the consumption of the liquid pressurecorresponding to the brake operation, irrespective of the detectionvalue detected by the pressure detector 11, as in thepreviously-described first embodiment. Thus, the frequency of operationof the liquid pump 9 can be suppressed to the minimum and, moreover, asufficient liquid pressure can be insured by the pressure tank 10 toprevent a reduction in brake assisting force.

FIGS. 13 and 14 illustrate a modification to the second embodiment. Thedriving means 54 has a map previously established therein as shown inFIG. 13, in which the driving time T₃ for the liquid pump 9 isdetermined in accordance with the vehicle speed V_(ON) at the start of abraking operation. During braking at a larger vehicle speed V_(ON), alarger braking force is required, and the amount of liquid pressureconsumed is larger. Therefore, in this map, the driving time T₃ isdetermined to be gradually larger, as the vehicle speed V_(ON) islarger.

If it is decided by the normal-state detecting means 44₂ that thepressure detector 11 is abnormal, a driving signal sustained for adriving time T₃ determined by a vehicle speed V_(ON), is outputted fromthe driving means 54 at the start of a braking force. Even if thepressure detector 11 gets out of order, the liquid pump 9 can beoperated in correspondence to the amount of liquid pressure consumed,thereby insuring a sufficient liquid pressure in the accumulator 10 toprevent a reduction in brake assisting force.

Although the embodiments of the present invention have been described indetail, it will be understood that the present invention is not limitedto these embodiments, and various modifications in design can be madewithout departing from the spirit and scope of the invention defined inclaims.

For example, the present invention can be applied to a negative pressureboosting type brake system comprising a liquid pump functioning as anegative pressure pump, and a pressure tank for storing a negativepressure therein instead of the described accumulator.

What is claimed is:
 1. A fluid pressure boosting type brake systemcomprising a fluid pressure source including a fluid pump and a pressuretank connected to said pump, and a control valve capable of controllingan output pressure from said fluid pressure source to a fluid pressurecorresponding to a degree of brake operation to output the same,whereinsaid system further includes a brake operation detecting meansfor detecting a brake operation, and a consumed-pressure correspondencedriving means for outputting a driving signal indicative of a command todrive the fluid pump for each preset time for a predetermined period,while the degree of brake operation is detected by said brake operationdetecting means.
 2. A fluid pressure boosting type brake systemaccording to claim 1, further includinga pressure detector for detectinga fluid pressure in said pressure tank, a detected-pressurecorrespondence driving means provided in parallel to saidconsumed-pressure correspondence driving means and capable of outputtinga driving signal indicative of a command to drive the fluid pump inaccordance with a detection value detected by said pressure detector,and a prohibiting-signal outputting means for outputting a prohibitingsignal indicative of a command to prohibit the output of said drivingsignal from said consumed-pressure correspondence driving means in astate in which said detected-pressure correspondence driving means canoutput the driving signal.
 3. A fluid pressure boosting type brakesystem according to claim 2, further including power circuitsindividually connected to said consumed-pressure correspondence drivingmeans and said detected-pressure correspondence driving means,respectively.